substage of immediately preceded by developmental stage dorsal closure stage embryonic stage 15 late embryonic stage embryonic stage 16 Stage 16 begins when the intersegmental grooves can be distinguished at mid-dorsal level, and ends when the dorsal ridge (frontal sac) has overgrown the tip of the clypeolabrum, which is thereby enclosed in the atrium. During this stage the ventral cord retracts to about 60% egg length. Duration at 25 degrees C: approximately 180 minutes (780-960 minutes after egg laying). FlyBase_development_CV FBdv:00005334 Temporal ordering number - 380.